Power conversion device

ABSTRACT

An increase in leakage current when a reverse voltage is applied to reverse-blocking insulated gate bipolar transistors is suppressed, thus reducing a loss resulting from the leakage current. A power conversion device includes a bidirectional switch formed by connecting two reverse-blocking insulated gate bipolar transistors having reverse breakdown voltage characteristics in reverse parallel. A control circuit is configured so as to output command signals for bringing the gates of the reverse-blocking insulated gate bipolar transistors, to which a reverse voltage is applied, into an on state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/JP2013/052318, filed on Feb. 1, 2013, which is based on and claimspriority to Japanese Patent Application No. JP 2012-081718, filed onMar. 30, 2012. The disclosure of the Japanese priority application andthe PCT application in their entirety, including the drawings, claims,and the specification thereof, are incorporated herein by reference.

BACKGROUND

1. Field of the Invention

Embodiments of the present invention relate to a power conversion deviceusing a bidirectional switch formed by connecting reverse-blockinginsulated gate bipolar transistors in reverse parallel.

2. Description of the Background

A bidirectional switch formed by connecting reverse-blocking insulatedgate bipolar transistors (RB-IGBTs) in reverse parallel, as it has lowloss characteristics, is put to practical use in a power conversiondevice such as an inverter or a converter, as for example, shown inJapanese Patent documents JP-A-2007-288958 and JP-A-2012-029429.

The reverse-blocking insulated gate bipolar transistor is such that thesize of leakage current when an on signal is given to the gate in acondition in which a reverse voltage is applied between the collectorand emitter differs from the size of leakage current when an off signalis given to the gate in the same condition, and the latter is larger. Anincrease in the leakage current when the reverse voltage is appliedcauses an increase in loss. Further, the increase in loss leads to adecrease in the reliability of the reverse-blocking insulated gatebipolar transistor and a reduction in the conversion efficiency of thepower conversion device.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a power conversion device whereinit is possible to suppress an increase in leakage current when a reversevoltage is applied, and thus reduce a loss resulting from the leakagecurrent.

According to an embodiment of the invention, a power conversion deviceincludes a bidirectional switch formed by connecting tworeverse-blocking insulated gate bipolar transistors, having reversebreakdown voltage characteristics, in reverse parallel, wherein aconfiguration is such that gate drive signals generated based on commandsignals output from a control circuit are given one to each of thereverse-blocking insulated gate bipolar transistors, and in order tosolve the previously described problem, the control circuit isconfigured so as to output, as the command signals, command signals forbringing the gates of the reverse-blocking insulated gate bipolartransistors, to which a reverse voltage is applied, into an on state.

In an embodiment which carries out three or more levels of powerconversions, one phase leg of power conversion circuit is configured soas to include a direct current power source having a positive electrode,middle electrode, and negative electrode; a first semiconductor switchelement to which a diode is connected in reverse parallel, and thecollector of which is connected to the positive electrode of the directcurrent power source; a second semiconductor switch element to which adiode is connected in reverse parallel, and the emitter of which isconnected to the negative electrode of the direct current power source;and the bidirectional switch, one end of which is connected to theconnection point of the emitter of the first semiconductor switchelement and the collector of the second semiconductor switch element,and the other end of which is connected to the middle electrode of thedirect current power source.

It is possible to apply, for example, an insulated gate bipolartransistor to the first and second semiconductor switch elements.

In another embodiment, one phase leg of power conversion circuit isconfigured so as to include a direct current power source; a first pairof the bidirectional switches connected in series between the positiveelectrode and negative electrode of the direct current power source; anda second pair of the bidirectional switches connected in series betweenthe positive electrode and negative electrode of the direct currentpower source.

In still another embodiment, the bidirectional switches are connected soas to configure a matrix converter.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram showing a configuration example of asingle-phase three-level power conversion device according to theinvention.

FIG. 2 is a circuit diagram showing a configuration example of a gatedrive circuit.

FIGS. 3A, 3B, 3C, and 3D show examples of gate drive signals in aswitching mode B.

FIG. 4 is a diagram showing a path of a current flowing through a loadbased on the gate signals of FIG. 3.

FIGS. 5A, 5B, 5C, and 5D show other examples of the gate drive signalsin the switching mode B.

FIG. 6 is a diagram showing a path of a current flowing through the loadbased on the gate signals of FIG. 5.

FIGS. 7A, 7B, 7C, and 7D show examples of gate drive signals in aswitching mode C.

FIG. 8 is a diagram showing a path of a current flowing through the loadbased on the gate signals of FIG. 7.

FIGS. 9A, 9B, 9C, and 9D show other examples of the gate drive signalsin the switching mode C.

FIG. 10 is a diagram showing a path of a current flowing through theload based on the gate signals of FIG. 9.

FIG. 11 is a circuit diagram showing a configuration example of athree-phase three-level power conversion device according to theinvention.

FIG. 12 is a circuit diagram showing a configuration example, and a pathof a drive current, of a single-phase two-level power conversion deviceaccording to the invention.

FIG. 13 is a circuit diagram showing a path of a recovery current in thepower conversion device of FIG. 12.

FIG. 14 is a diagram showing another path of the drive current in thepower conversion device of FIG. 12.

FIG. 15 is a diagram showing another path of the recovery current in thepower conversion device of FIG. 12.

FIG. 16 is a chart showing gate drive signals in the power conversiondevice of FIG. 12.

FIG. 17 is a circuit diagram showing a configuration example of athree-phase two-level power conversion device according to theinvention.

FIG. 18 is a circuit diagram showing a configuration example of a matrixconverter according to the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 is a circuit diagram showing a configuration example of asingle-phase three-level power conversion device (inverter) according toan embodiment of the invention. The power conversion device includes adirect current power source PS, an arm pair AP, and a bidirectionalswitch (alternating current switch) SW.

The power source PS includes capacitors C1 and C2 connected in series.The terminal voltages of the capacitors C1 and C2 are both Vcc2.Consequently, a voltage Vcc1 between the positive electrode and negativeelectrode of the power source PS is 2×Vcc2.

The arm pair AP includes semiconductor switch elements T1 and T2connected in series and free wheel diodes D1 and D2 connected inparallel to the respective semiconductor switch elements T1 and T2. Inthis embodiment, an insulated gate bipolar transistor (IGBT) is used asthe semiconductor switch elements T1 and T2, but in place of this, it isalso possible to use another semiconductor switch element.

The collector of the upper arm side semiconductor switch element T1 isconnected to the positive electrode of the power source PS via aterminal P, and the emitter of the lower arm side semiconductor switchelement T2 is connected to the negative electrode of the power source PSvia a terminal N. Also, the midpoint of the arm pair AP, which is theconnection point of the emitter of the semiconductor switch element T1and the collector of the semiconductor switch element T2, is connectedto an output terminal U.

The bidirectional switch SW, which includes two reverse-blockinginsulated gate bipolar transistors T3 and T4 connected in reverseparallel, is connected between the middle electrode of the power sourcePS connected to a terminal M and the midpoint of the arm pair AP.

Hereafter, the reverse-blocking insulated gate bipolar transistor willbe abbreviated to “RB-IGBT.”

As is well known, the RB-IGBT differs from a standard IGBT by includingreverse breakdown voltage capability. The bidirectional switch SWconfigured of these kinds of RB-IGBTs has the advantage that there is noneed for a diode for blocking a reverse current, because of which noloss due to the diode occurs. The bidirectional switch SW and arm pairAP can be integrated (modularized) together.

Gate drive circuits GDU1 and GDU2 are connected to the gates of thesemiconductor switch elements T1 and T2, respectively, and gate drivecircuits GDU3 and GDU4 are connected to the gates of the RB-IGBTs T3 andT4, respectively. The gate drive circuits GDU1 to GDU4, based on commandsignals S1 to S4 output from a control circuit CC, generatecorresponding gate drive signals.

A well-known configuration can be used for the gate drive circuits GDU1to GDU4, and one example thereof is shown in FIG. 2. The gate drivecircuits GDU1 to GDU4 each include a photocoupler PC, a buffer circuitBU formed of transistors T4 and T5, a positive side power source E1, anegative side power source E2, and a resistor R. The command signals S1to S4 from the control circuit CC shown in FIG. 1 are input one into thephotocoupler PC of each respective gate drive circuit GDU1 to GDU4.

The buffer circuit BU of each gate drive circuit GDU1 to GDU4, when eachrespective command signal S1 to S4 provides a gate on command, outputs agate drive signal which turns on the gate by the on operation of thetransistor T4, and when each respective command signal S1 to S4 providesa gate off command, outputs a gate drive signal which turns off the gateby the on operation of the transistor T5.

The voltage value of the gate drive signal which turns on the gate issubstantially equal to the voltage (+15V) of the positive side powersource E1, and the voltage value of the gate drive signal which turnsoff the gate is substantially equal to the output voltage (−15V) of thenegative side power source E2.

The RB-IGBTs T3 and T4 configuring the bidirectional switch SW each havethe property that a leakage current increases due to hole reinjectionfrom the emitter when a reverse voltage is being applied between thecollector and emitter. In order to avoid the leakage current increase, agate on signal may be applied to the gates of the RB-IGBTs T3 and T4when the reverse voltage is being applied to the RB-IGBTs T3 and T4.That is, by giving the on signal to the gates, electrons pass through ann+channel and reach the emitters, in other words, there is no more holereinjection, meaning that the increase in leakage current is suppressed.

The following table shows, by switching mode, the forms of the gatedrive signals given to the semiconductor switch elements T1 and T2 andRB-IGBTs T3 and T4. According to the gate drive signals shown in thetable, the increase in leakage current of the RB-IGBTs T3 and T4 issuppressed, as will be described hereafter.

In the table, ON denotes that the gates are turned on, “OFF” denotesthat the gates are turned off, and “SW” denotes that the gates areturned on and off.

TABLE 1 SW mode Load L T1 T2 T3 T4 A U-N SW OFF OFF OFF P-U OFF SW OFFOFF B P-U OFF OFF SW ON U-N OFF OFF ON SW C M-U SW OFF OFF ON M-U OFF SWON OFF

The power conversion device shown in FIG. 1 operates in the followingway by the gate drives shown in the table.

Switching Mode A

Firstly, a description will be given of a case in which a load L isconnected between the terminal U and terminal N (refer to the solidline), and the load L is driven by the upper arm side switch element T1.In this case, the control circuit CC outputs a signal S1 providing an“SW” command and signals S2 to S4 providing an “OFF” command. In thiscase, the signal S1 is a signal formed of a modulated (for example, apulse-width modulated) pulse train.

In accordance with this, the gate drive circuit GDU1 outputs a gatedrive signal which turns on and off the gate of the switch element T1,and the gate drive circuits GDU2, GDU3, and GDU4 output gate drivesignals which turn off the gates of the switch element T2, RB-IGBT T3,and RB-IGBT T4, respectively. As a result of this, only the switchelement T1 is in on and off operation, and the switch element T2,RB-IGBT T3, and RB-IGBT T4 are in an off state.

When the switch element T1 is in on and off operation, a current I_(L)flows through the load L in the on period, and a recovery current I_(R)flows via the free wheel diode D2 in the off period.

Next, a description will be given of a case in which the load L isconnected between the terminal P and terminal U (refer to thedashed-dotted line), and the load L is driven by the lower arm sideswitch element T2. In this case, the control circuit CC outputs signalsS1, S3, and S4 providing an “OFF” command and a signal S2 providing an“SW” command.

In accordance with this, only the switch element T2 is in on and offoperation, and the switch element T1, RB-IGBT T3, and RB-IGBT T4 are inan off state.

When the switch element T2 is in on and off operation, a load current(not shown) flows in the on period, and a recovery current (not shown)flows through the free wheel diode D1 in the off period.

Switching Mode B

Firstly, a description will be given of a case in which the load L isconnected between the terminal P and terminal U, and the load L isdriven by the RB-IGBT T3 of the switch SW. In this case, the controlcircuit CC outputs signals S1 and S2 providing an “OFF” command, asignal S3 providing an “SW” command, and a signal S4 providing an ONcommand.

In accordance with this, the gate drive circuits GDU1 and GDU2respectively output the kinds of gate drive signals shown in FIG. 3A andFIG. 3B, the gate drive circuit GDU3 outputs the kind of gate drivesignal illustrated in FIG. 3C, and the gate drive circuit GDU4 outputsthe kind of gate drive signal shown in FIG. 3D. As a result of this, theRB-IGBT T3 is in on and off operation, and the switch elements T1 and T2are both in an off state. At this time, the RB-IGBT T4 is not turned onalthough being given the gate drive signal which turns on the gate. Thisis because the terminal voltage Vcc2 of the capacitor C1 is beingapplied between the collector and emitter of the RB-IGBT T4 via the loadL in a reverse direction.

The current I_(L) flows through the load L in the on period of theRB-IGBT T3, as shown in FIG. 4 in which the switch element T2 andcapacitor C2 are omitted. The voltage applied between the collector andemitter of the RB-IGBT T3 is not Vcc1 but the terminal voltage Vcc2(Vcc1/2) of the capacitor C1. The recovery current I_(R) flows via thefree wheel diode D1 in the off period of the RB-IGBT T3.

As the gate drive signal which turns on the gate is input into theRB-IGBT T4 between the collector and emitter of which is applied thereverse voltage Vcc2, as heretofore described, the previously describedincrease in leakage current due to hole reinjection is suppressed, and aloss due to the leakage current is reduced.

Next, a description will be given of a case in which the load L isconnected between the terminal U and terminal N, and the load L isdriven by the switch element T4 of the switch SW. In this case, thecontrol circuit CC outputs control signals S1 and S2 providing an “OFF”command, a control signal S3 providing an ON command, and a controlsignal S4 providing an “SW” command.

In accordance with this, the gate drive circuits GDU1 and GDU2respectively output the kinds of gate drive signals shown in FIGS. 5Aand 5B, the gate drive circuit GDU3 outputs the kind of gate drivesignal shown in FIG. 5C, and the gate drive circuit GDU4 outputs thekind of gate drive signal (a signal wherein the signal shown in FIG. 3Cis inverted) shown in FIG. 5D. As a result of this, the RB-IGBT T4 is inon and off operation, and the switch elements T1 and T2 are in an offstate. The RB-IGBT T3, as a reverse voltage is being applied between thecollector and emitter thereof, is in an off state.

The current I_(L) flows through the load L in the on period of theRB-IGBT T4, as shown in FIG. 6 in which the switch element T1 andcapacitor C1 are omitted, but the size of the load current I_(L) is also½ of the previously described load current I_(L) in the switching modeA. The recovery current I_(R) flows via the free wheel diode D2 in theoff period of the RB-IGBT T4.

As the gate drive signal which turns on the gate is input into the gateof the RB-IGBT T3 between the collector and emitter of which is appliedthe reverse voltage Vcc2, as previously described, the increase inleakage current due to hole reinjection is suppressed.

Switching Mode C

Firstly, a description will be given of a case in which the load L isconnected between the terminal M and terminal U (not shown in FIG. 1),and the load L is driven by the upper arm side switch element T1. Inthis case, the control circuit CC outputs a signal S1 providing an “SW”command, signals S2 and S3 providing an “OFF” command, and a signal S4providing an ON command.

In accordance with this, the gate drive circuit GDU1 outputs the kind ofgate drive signal shown in FIG. 7A, the GDU2 and GDU3 respectivelyoutput the kinds of gate drive signals shown in FIGS. 7B and 7C, and thegate drive circuit GDU4 outputs the kind of gate drive signal shown inFIG. 7D. As a result of this, the switch element T1 is in on and offoperation, and the switch element T2 and RB-IGBT T3 are both in an offstate.

The current I_(L) flows through the load L in the on period of theswitch element T1, as shown in FIG. 8 in which the switch element T2 andcapacitor C2 are omitted, but the size of the load current I_(L) is ½ ofthe previously described load current I_(L) in the switching mode A.

The RB-IGBT T4 is in an off state in the on period of the switch elementT1, and causes the recovery current I_(R) to flow in the off period ofthe switch element T1. Also, the reverse voltage Vcc2 is applied to theRB-IGBT T4 in the on period of the switch element T1, but at this time,the gate on signal shown in FIG. 7D is input into the RB-IGBT T4,meaning that the previously described increase in leakage current due tohole reinjection is suppressed, and a loss due to the leakage current isreduced.

Next, a description will be given of a case in which the load L isconnected between the terminal U and terminal N in the same way asheretofore described, and the load L is driven by the lower arm sideswitch element T2. In this case, the control circuit CC outputs signalsS1 and S4 providing an “OFF” command, a signal S2 providing an “SW”command, and a signal S3 providing an ON command.

In accordance with this, the GDU1 and GDU4 respectively output the kindsof gate drive signals shown in FIGS. 9A and 9D, the gate drive circuitGDU2 outputs the kind of gate drive signal illustrated in FIG. 9B (asignal wherein the signal shown in FIG. 7A is inverted), and the GDU3outputs the kind of gate drive signal shown in FIG. 9C. As a result ofthis, the switch element T2 is in on and off operation, and the switchelement T1 and RB-IGBT T4 are both in an off state.

The current I_(L) flows through the load L in the on period of theswitch element T2, as shown in FIG. 10 in which the switch element T1and capacitor C1 are omitted.

The RB-IGBT T3 is in an off state in the on period of the switch elementT2, and causes the recovery current I_(R) to flow in the off period ofthe switch element T2. Also, the reverse voltage Vcc2 is applied to theRB-IGBT T3 in the on period of the switch element T2, but at this time,the gate on signal shown in FIG. 9C is input into the RB-IGBT T3,meaning that the previously described increase in leakage current due tohole reinjection is suppressed.

As heretofore described, according to the power conversion deviceaccording to an embodiment of the invention, when the reverse voltageVcc2 is applied to the RB-IGBT T3 and RB-IGBT T4 configuring thebidirectional switch SW, the gate drive signals which turn on the gatesare input into the RB-IGBT T3 and RB-IGBT T4. Consequently, the increasein leakage current due to hole reinjection is suppressed, and powerconversion efficiency is improved.

FIG. 11 shows a three-phase three-level power conversion deviceincluding three phases leg of arm pairs AP and bidirectional switches SWshown in FIG. 1. In the power conversion device, arm pairs AP1, AP2, andAP3 have the same configuration as the arm pair AP shown in FIG. 1, andbidirectional switches SW1, SW2, and SW3 have the same configuration asthe bidirectional switch SW shown in FIG. 1. The arm pairs AP1, AP2, andAP3 can be integrated (modularized) together with the respectivebidirectional switches SW1, SW2, and SW3. Reference sign L_(O)represents a filter reactor, and reference sign L′ represents athree-phase load.

In a power conversion device according to an embodiment the invention,there is a case in which a reverse voltage is applied to RB-IGBTsconfiguring each bidirectional switch SW1 to SW3. In this case, anunshown control circuit outputs gate drive signals which turn on thegates of the RB-IGBTs to which the reverse voltage is applied. By sodoing, an increase in leakage current in the RB-IGBTs is suppressed, andpower conversion efficiency is improved.

In both the power conversion device according to the invention and thepower conversion shown in FIG. 1, it is possible to obtain three levelsof voltage outputs, but in a power conversion device (for example, referto JP-A-2011-72118) wherein it is possible to obtain a larger number oflevels of voltage outputs, it is also possible to improve powerconversion efficiency by adopting a configuration wherein the gates ofRB-IGBTs to which a reverse voltage is being applied are turned on.

FIG. 12 is a circuit diagram showing an embodiment of a single-phasetwo-level power conversion device (inverter) according to an embodimentthe invention. The power conversion device has a configuration wherein apair of bidirectional switches SW10 and SW30 connected in series and apair of bidirectional switches SW20 and SW40 connected in series areconnected in parallel between the positive electrode and negativeelectrode of a direct current power source PS′ formed of a capacitor,and a single-phase load L is connected between the series connectionpoint of the bidirectional switches SW10 and SW30 and the seriesconnection point of the bidirectional switches SW20 and SW40.

Each pair of RB-IGBT T11 and RB-IGBT T12 configuring the bidirectionalswitch SW10, RB-IGBT T21 and RB-IGBT T22 configuring the bidirectionalswitch SW20, RB-IGBT T31 and RB-IGBT T32 configuring the bidirectionalswitch SW30, and RB-IGBT T41 and RB-IGBT T42 configuring thebidirectional switch SW40, corresponds to the RB-IGBT T1 and RB-IGBT T2configuring the bidirectional switch SW1 shown in FIG. 1.

Gate drive circuits GDU11 and GDU12 are connected to the respectiveRB-IGBTs T11 and T12, gate drive circuits GDU21 and GDU22 are connectedto the respective RB-IGBTs T21 and T22, gate drive circuits GDU31 andGDU32 are connected to the respective RB-IGBTs T31 and T32, and gatedrive circuits GDU41 and GDU42 are connected to the respective RB-IGBTsT41 and T42.

The gate drive circuits of FIG. 12 have the same configuration as thegate drive circuits GDU1 to GDU4 shown in FIG. 2, and command signalsfrom a control circuit CC′ are input one into each of the gate drivecircuits.

Hereafter, a description will be given of an operation of the powerconversion device according to this embodiment of the invention. Thecontrol circuit CC′ outputs command signals S11, S12, S21, S22, S31,S32, S41, and S42.

That is, the control circuit CC′ outputs command signals such as togenerate gate drive signals which turn on the gates of the RB-IGBTs T11,T22, T32, and T41, and gate drive signals which turn off the gates ofthe RB-IGBTs T12, T21, T31, and T42, in the period (1) shown in FIG. 16.

As a result of this, the RB-IGBTs T11 and T41 are turned on, and as wellas a load drive current I_(A) flowing through the path shown in FIG. 12,a reverse voltage is applied between the collectors and emitters of theRB-IGBTs T22 and T32. As the gate drive signals which turn on the gatesare input into the RB-IGBTs T22 and T32 to which the reverse voltage isapplied, as shown by the hatched lines, an increase in leakage currentdue to hole reinjection is suppressed.

Next, the control circuit CC′ outputs command signals such as togenerate gate drive signals which turn on the gates of the RB-IGBTs T12,T22, T32, and T42, and gate drive signals which turn off the gates ofthe RB-IGBTs T11, T21, T31, and T41, in the period (2) shown in FIG. 16.

As a result of this, the RB-IGBTs T22 and T32 are turned on, and as wellas a recovery current I_(B) flowing through the path shown in FIG. 13, areverse voltage is applied between the collectors and emitters of theRB-IGBTs T12 and T42. As the gate drive signals which turn on the gatesare input into the RB-IGBTs T12 and T42 to which the reverse voltage isapplied, as shown in the hatched lines, an increase in leakage currentdue to hole reinjection is suppressed.

The control circuit CC′ outputs command signals such as to generate gatedrive signals which turn on the gates of the RB-IGBTs T12, T21, T31, andT42, and gate drive signals which turn off the gates of the RB-IGBTsT11, T22, T32, and T41, in the period (3) shown in FIG. 16.

As a result of this, the RB-IGBTs T21 and T31 are turned on, and as wellas a recovery current I_(C) flowing through the path shown in FIG. 14, areverse voltage is applied between the collectors and emitters of theRB-IGBTs T12 and T42. As the gate drive signals which turn on the gatesare input into the RB-IGBTs T12 and T42 to which the reverse voltage isapplied, as shown in the hatched lines, the increase in leakage currentdue to hole reinjection is suppressed.

Next, the control circuit CC′ outputs command signals such as togenerate gate drive signals which turn on the gates of the RB-IGBTs T12,T22, T32, and T42, and gate drive signals which turn off the gates ofthe RB-IGBTs T11, T21, T31, and T41, in the period (4) shown in FIG. 16.

As a result of this, the RB-IGBTs T12 and T42 are turned on, and as wellas a recovery current I_(D) flowing through the path shown in FIG. 15, areverse voltage is applied between the collectors and emitters of theRB-IGBTs T22 and T32. As the gate drive signals which turn on the gatesare input into the RB-IGBTs T22 and T32 to which the reverse voltage isapplied, as shown in the hatched lines, the increase in leakage currentdue to hole reinjection is suppressed.

FIG. 17 is a circuit diagram showing a three-phase two-level powerconversion device (inverter) according to an embodiment of theinvention. The power conversion device, being such that the powerconversion device shown in FIG. 12 is extended to a three-phase use soas to be applied to a three-phase load L′, includes a pair ofbidirectional switches SW50 and SW80, a pair of bidirectional switchesSW60 and SW90, and a pair of bidirectional switches SW70 and SW100, eachof which is connected in series between the positive electrode andnegative electrode of a direct current source PS′.

There is a case in which a reverse voltage is applied between thecollectors and emitters of some of RB-IGBTs configuring thebidirectional switches SW50 to SW100.

RB-IGBTs to which the reverse voltage is applied are known in advancefrom a gate control sequence. Therefore, an unshown control circuitoutputs command signals such as to generate gate drive signals whichturn on the gates of the RB-IGBTs in order to suppress an increase inleakage current of the RB-IGBTs to which the reverse voltage is applied.By so doing, a loss due to the increase in leakage current of theRB-IGBTs to which the reverse voltage is applied is reduced.

FIG. 18 is a circuit diagram showing a configuration example of a powerconversion device according to an embodiment of the invention which isapplied to a matrix converter. The power conversion device has aconfiguration wherein nine bidirectional switches SW110, SW120, SW130,SW140, SW150, SW160, SW170, SW180, and SW190 are connected between athree-phase alternating current power source AC-PS and a three-phaseload L′.

In the power conversion device too, there is a case in which a reversevoltage is applied between the collectors and emitters of some ofRB-IGBTs configuring the bidirectional switches SW110 to SW190.Therefore, an unshown control circuit, in order for gate on signals tobe input into the gates of switch elements to which the reverse voltageis applied, outputs control signals which instruct gate drive circuitscorresponding to the switch elements to turn on the gates of the switchelements. As a result of this, the switch elements to which the reversevoltage is applied are such that an increase in leakage current due tohole reinjection is suppressed, and a loss due to the increase inleakage current is reduced.

According to embodiments of the invention, as signals which turn on thegates are given to the gates of reverse-blocking insulated gate bipolartransistors in a condition in which a reverse voltage is applied betweenthe collectors and emitters, an increase in leakage current accompanyingthe application of the reverse voltage is suppressed. As a result ofthis, it is possible to reduce a loss resulting from the leakagecurrent, and thus improve the reliability of the reverse-blockinginsulated gate bipolar transistors and the conversion efficiency of thepower conversion device.

Also, as command signals for bringing the gates of the reverse-blockinginsulated gate bipolar transistors, to which the reverse voltage isapplied, into an on state are output from a control circuit, there isalso the advantage of there being no need for means for detecting thereverse-blocking insulated gate bipolar transistors to which the reversevoltage is applied.

1. A power conversion device comprising: a bidirectional switchcomprising two reverse-blocking insulated gate bipolar transistors,having reverse breakdown voltage characteristics, connected in reverseparallel, a configuration being such that gate drive signals generatedbased on command signals output from a control circuit are given one toeach of the reverse-blocking insulated gate bipolar transistors, thecontrol circuit being configured so as to output, as the commandsignals, command signals for bringing the gates of the reverse-blockinginsulated gate bipolar transistors, to which a reverse voltage isapplied, into an on state.
 2. The power conversion device according toclaim 1, wherein the device is configured to carry three or more levelsof power conversions, and wherein one phase leg of power conversioncircuit includes: a direct current power source having a positiveelectrode, a middle electrode, and a negative electrode; a firstsemiconductor switch element to which a diode is connected in reverseparallel, the collector of the first semiconductor switch element beingconnected to the positive electrode of the direct current power source;a second semiconductor switch element to which a diode is connected inreverse parallel, the emitter of the second semiconductor switch elementbeing connected to the negative electrode of the direct current powersource; and the bidirectional switch, one end of which is connected tothe connection point of the emitter of the first semiconductor switchelement and the collector of the second semiconductor switch element,and the other end of which is connected to the middle electrode of thedirect current power source.
 3. The power conversion device according toclaim 2, wherein the first and second semiconductor switch elements areinsulated gate bipolar transistors.
 4. The power conversion deviceaccording to claim 1, wherein one phase leg of power conversion circuitincludes: a direct current power source; a first pair of thebidirectional switches connected in series between a positive electrodeand a negative electrode of the direct current power source; and asecond pair of the bidirectional switches connected in series betweenthe positive electrode and the negative electrode of the direct currentpower source.
 5. The power conversion device according to claim 1,wherein a plurality of the bidirectional switches are connected so as toconfigure a matrix converter.
 6. A power conversion device comprising: afirst reverse-blocking insulated gate bipolar transistor; a secondreverse-blocking insulated gate bipolar transistor connected in reverseparallel with the first reverse-blocking insulated gate bipolartransistor; a first gate driver connected to the first reverse-blockinginsulated gate bipolar transistor; and a second gate driver connected tothe second reverse-blocking insulated gate bipolar transistor, whereinthe first gate driver is configured to provide, while a reverse voltageis applied to the first reverse-blocking insulated gate bipolartransistor, a signal to a gate of the first reverse-blocking insulatedgate bipolar transistor to bring the gate into an on state, and thesecond gate driver is configured to provide, while a reverse voltage isapplied to the second reverse-blocking insulated gate bipolartransistor, a signal to a gate of the second reverse-blocking insulatedgate bipolar transistor to bring the gate into an on state.
 7. The powerconversion device according to claim 6, further comprising a controlcircuit, wherein the first and second gate drivers provide the signalsto the gates in response to respective command signals from the controlcircuit.